Many integrated circuits include on-chip circuitry to generate a voltage having a magnitude greater than and/or that is negative relative to a selected power supply voltage. Such voltage may be used to power portions of the circuitry contained on the integrated circuit. For example, semiconductor memories, such as FLASH or EEPROM memories, may require write and/or erase voltages that are higher than the voltage needed to power the remainder of the circuitry included on the integrated circuit.
Charge pumps are one class of such voltage boosting and/or inverting circuits. Charge pumps are generally implemented as capacitive voltage multiplier circuits. Charge pumps use switch isolated capacitors to convert an input voltage to an output voltage that may be higher than, or negative relative to, the input voltage. In a charge pump, the switches coupled to a capacitor are operated in sequence to first charge the capacitor from the input voltage and then transfer the charge to the output. A charge pump circuit may include a number of stages, each of which may boost or negate the voltage output by the previous stage.